General reflective type liquid crystal projection optical engines have different architectures. For example, companies such as JVC, Philips, Color Link, RDI, and Aurora System produce reflective type liquid crystal projection devices of different structures. Almost all the structures adopt an X-prism. Color Link and RDI adopt their own color selectors to achieve the object of light-splitting projection.
Generally, reflective type liquid crystal projection devices mainly adopt the X-prism architecture to let the three primary colors of red (R), green (G), and blue (B) enter three different sets of polarization beam splitters (PBS) and then combine together. Three light beams are the common design idea. They differ only in variation of light projection system. Different light projection systems have different usage efficiencies of light energy and different sizes of occupied volume. However, the above projection devices have more complicated structures and require more optical components. Besides, it is necessary to take different polarization states of the same color light into account for light splitting, and the requirements for transmission and reflection differ. Therefore, the manufacturing is more difficult, and the production cost is higher. Furthermore, the optimum usage efficiencies of the three primary colors R, G and B can't be accomplished.
For projection systems adopting prism type beam combiners or PBS, the weight is larger and the material cost is higher. Moreover, because light travels a longer path in the prism type components, the accumulated total optical path difference will be large due to variation and non-uniformity of refractive index of components owing to heat, hence causing distortion of image. Furthermore, because prism type components have an inferior heat-radiating performance, it is difficult to solve the thermal effects.
Accordingly, the present invention aims to propose a reflective type light valve projection device, which can effectively make use of space, shrink the volume, and simplify the manufacturing process for lowering the production cost.